The Use of a Magnetic Field and Magnetic Force as a Means to Improve the Quality of Protein Crystals - Molecules: Nucleation, Aggregation and Crystallization - page 215

experiences an upward magnetic force amounting to 30% of gravity. Thus,
the net force becomes 70% of gravity. Similarly, at a lower position,
100 mm downward from the magnet center, the magnetic field becomes
6 T (symmetrical with respect to the center), with a field gradient of
about 66.7 T/m but weaker in the lower direction, with a field-field gra-
dient product of 400 T 2 /m. The minus sign means that the force for a

diamagnetic substance is downward. Its strength also amounts to 30% of
gravity, but in this case the direction is the same as gravity, leading to a
net force of 1.3 times gravity.
The protein used to compare the results of crystal growth was fructose
1,6-bisphosphatase, purified from a Chinese snake muscle. This is a pro-
tein involved in gluconeogenesis. The solution, supersaturated by the
addition of MgCl 2 and polyethylene glycol 3350, was divided into batches,
which were placed at the “middle” position at the magnet center, at the
“upper” and “lower” positions defined above, and at a position outside of
the magnet where both the magnetic field and the magnetic force were
absent. The crystals grown after two to six days were evaluated with
X-rays using a resolution that gave an S/N ratio of two on 1

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oscillation
photographs. Owing to magnetic orientation, many crystals grown in the
magnetic fields (of trigonal symmetry) “stood” on a narrower face. The
results and reproducibility are shown in Table 1.
It was found that the crystals that grew at the “upper” position showed
the best resolution with least fluctuation among the crystals. The resolu-
tion was better than the crystals grown at the magnet center, and also than
those grown outside the magnet. Note that the magnet center provided the
strongest magnetic field, but the crystals were better when the upward
magnetic force was superimposed on the (weaker than the center) mag-
netic field of 6 T. We can conclude that the magnetic force, an independ-
ent environment that a magnet can provide in addition to the magnetic
field, can be used beneficially to grow better quality crystals.
The superconducting magnet that we used could not provide sufficient
upward magnetic force to cancel gravity entirely. But Yin et al . (2004)
grew hen egg-white lysozyme crystals (orthorhombic form) in a strong
and upward magnetic force that did totally cancel gravity. The crystals

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